Guangda Li

Enhanced Lithium Storage Performances of Hierarchical Hollow MoS2 Nanoparticles Assembled from Nanosheets

MoS(2), because of its layered structure and high theoretical capacity, has been regarded as a potential candidate for electrode materials in lithium secondary batteries. But it suffers from the poor cycling stability and low rate capability. Here, hierarchical hollow nanoparticles of MoS(2) nanosheets with an increased interlayer distance are synthesized by a simple solvothermal reaction at a low temperature. The formation of hierarchical hollow nanoparticles is based on the intermediate, K(2)NaMoO(3)F(3), as a self-sacrificed template. These hollow nanoparticles exhibit a reversible capacity of 902 mA h g(-1) at 100 mA g(-1) after 80 cycles, much higher than the solid counterpart. At a current density of 1000 mA g(-1), the reversible capacity of the hierarchical hollow nanoparticles could be still maintained at 780 mAh g(-1). The enhanced lithium storage performances of the hierarchical hollow nanoparticles in reversible capacities, cycling stability and rate performances can be attributed to their hierarchical surface, hollow structure feature and increased layer distance of S-Mo-S. Hierarchical hollow nanoparticles as an ensemble of these features, could be applied to other electrode materials for the superior electrochemical performance.

Synthesis, characterization and application of carbon nanocages as anode materials for high-performance lithium-ion batteries

Carbon nanocages (CNCs) with diameters of about 200∼500 nm have been synthesized by a simple method. The electrochemical properties of the CNCs as anode materials were evaluated by discharge/charge measurement and electrochemical impedance spectroscopy. Results showed that the CNCs displayed excellent cycling performance and good rate capability with no noticeable capacity fading up to 50 cycles at current densities of 100, 300 and 500 mA g−1. Their electrochemical properties were significantly improved after annealing treatment of the CNCs at 600 °C. For example, the CNCs(2)-annealed exhibited much better electrochemical performance with a high reversible capacity of 520 mAh g−1 after 50 cycles at current density of 100 mA g−1. A discharge capacity of 380 mAh g−1 can be obtained after 50 cycles at high current density of 500 mA g−1. The results of the Raman, thermal gravimetric and electrochemical impedance analysis indicated that the graphitization degree, electronic conductivity and charge-transfer rate of the CNCs have been improved after annealing treatment.

High yield synthesis of novel boron nitride submicro-boxes and their photocatalytic application under visible light irradiation

In this study, hexagonal boron nitride submicro-boxes (BNMB) (0.50–1.4 μm) have been synthesized by using KBH4, NH4F and Zn in a stainless steel autoclave at 450 °C. The formation process was studied by XRD, TEM and EDS, and it is considered that the in situ formed KZnF3 intermediate cubes serve as templates for the formation of BNMB. The as-formed BNMB, with unique structural features, high specific surface area (∼86.9 m2 g−1) and good chemical properties, can be applied as a catalyst support for SnO2. The UV-Vis diffuse reflectance spectrum of SnO2/BNMB shows the absorption edge in the visible region (∼470 nm), making it suitable for photocatalytic application. The experimental result indicates that the SnO2/BNMB exhibited excellent photocatalytic activity on the degradation of methyl orange (MO), which was up to 92% after 30 min of visible-light (λ > 420 nm) irradiation. The good photocatalytic activity was attributed mainly to its suitable band gap energy, strong adsorption ability for MO, and effective charge separation at the SnO2/BNMB photocatalyst interface.

Hydrothermal synthesis of microscaled Cu@C polyhedral composites and their sensitivity to convergent electron beams.

Copper microparticles (2-5 um) encapsulated in carbonaceous shell polyhedral composites were mildly prepared via a one-pot hydrothermal process using copper nitrate, glucose, and sodium citrate at 150 degrees C, in which the glucose was found to play reducer and graphite source roles during the formation of these core-shell-like composites. Thermal stability results indicated that their weights remain almost unchanged below 240 degrees C in ambient atmosphere. It is interesting that the copper microparticles could be partially released out and translated into monodisperse Cu nanoparticles around the initial composites under the convergent electron beams in a transmission electron microscope (TEM). This phenomenon is an appealing discovery, which might endow the Cu@C composite with new functions; for example, it might be applied as a sensitive detector for the leakage of electron beams or other substances for the sake of being a safeguard. In addition, the corresponding hollow carbonaceous polyhedra were also obtained after the acid treatment, which might be used as a template to fabricate other kinds of polyhedra.